Not applicable.
Not Applicable.
The present invention relates to methods and devices for non-invasively monitoring the performance of implanted medical devices without requiring additional energy means such as x-ray, ultrasound, or telemetry. More specifically, the present invention relates to a method for detecting the activity of an implanted adjustable shunt valve using an acoustic monitoring device and system.
Shunt systems for directing body fluid from one region to another are known in the medical field. One application for such a shunt system is in the treatment of hydrocephalus, a condition where cerebrospinal fluid collects in the ventricles of the brain of a patient. Cerebrospinal fluid is produced by the ventricular system and is normally absorbed by the venous system. However, if the cerebrospinal fluid is not absorbed, the volume of cerebrospinal fluid increases thereby elevating the patient""s intracranial pressure. This excess cerebrospinal fluid can result in abnormally high epidural and intradural pressures. Left untreated, hydrocephalus can result in serious medical conditions, including subdural hematoma, compression of the brain tissue, and impaired blood flow.
To treat patients with hydrocephalus, shunt systems have been used to remove the excess cerebrospinal fluid and to discharge the fluid to another part of the patient""s body, such as the right atrium or peritoneal cavity. By draining the excess fluid, the elevated intracranial pressure is relieved. Generally, these fluid shunt systems include a valve mechanism for controlling or regulating the flow rate of fluid through the shunt system. The shunt systems often include a brain ventricular catheter in fluid communication with the valve mechanism. The ventricular catheter is inserted into a ventricle of the brain and a peritoneal catheter, which is also in fluid communication with the valve mechanism, is inserted into the peritoneal cavity of the patient for discharging the excess cerebrospinal fluid. The valve mechanisms of these shunt systems typically operate to permit fluid flow only once the fluid pressure reaches a certain threshold level. The fluid flow rate is proportional to the pressure at the valve mechanism. Thus, for a pressure slightly greater than the threshold or opening pressure, the flow rate is relatively low. As the pressure increases the flow rate through the shunt system concomitantly increases. At pressures significantly greater than the threshold pressure, a maximum flow rate for the system is reached. Fluid flow normally continues until the intracranial pressure has been reduced to a level less than the threshold pressure, subject to any hysteresis of the device.
The threshold or opening pressure that allows fluid flow through a shunt system must often be adjusted. For example, a surgeon may initially select a relatively low opening pressure to trigger fluid flow. Over time, the initial opening pressure may not be ideal. For example, it could lead to excess fluid flow, creating an undesirable overdrainage condition in which too much fluid is drained from the ventricle. Such a situation may give rise to a need to increase the opening pressure to produce a fluid flow rate that is balanced to avoid both excessive intracranial pressure and overdrainage conditions.
Because physiologies will vary over time and from one individual to another, some valve systems have been designed to be adjustable without requiring invasive procedures. These adjustable valves allow the clinician to customize the implanted valve mechanism""s opening pressure for a particular patient, without the need to surgically remove the implanted shunt system, adjust the valve mechanism, and then surgically implant the shunt system again. Such an adjustable valve system is described in, for example, U.S. Pat. Nos. 4,595,390, 4,615,691, 4772,257, and 5,928,182, all of which are hereby incorporated by reference. Commonly referred to as the Hakim programmable valve, the Hakim valve described in these patents is a differential pressure valve with very precise opening pressures determined by the force exerted on a ruby ball in a ruby seat. The pressure at which the valve opens can be adjusted non-invasively by the clinician by means of an externally applied rotating magnetic field. The valve opening pressure is adjusted by varying the spring tension exerted on the ruby ball. Applying an external magnetic field to energize the soft magnet stator components of the valve initiates the adjustment cycle. The magnetic field causes the rotor to rotate about a central axis. As the stator polarity is cycled, the rotor (cam) moves to different positions to align with the stator. These components perform together as a stepping motor. The spring rides along the cam; as the cam rotates clockwise or counter-clockwise, the spring tension increases or decreases, respectively. Other exemplary types of adjustable shunt valves are described in U.S. Pat. Nos. 5,637,038 and 5,643,194.
Current practice recommends an x-ray be taken after each valve adjustment to verify the new setting. The use of additional energy means to conventionally determine valve position, however, can often lead to undesirable complications. For instance, when magnetic fields are used for verifying valve position, metallic equipment within the clinical environment may interfere with the accuracy of information obtained through the use of these magnetic forces, leading to inaccurate readings.
There is thus a need for a non-invasive means of accurately verifying the position of an implanted adjustable valve within a patient so that repeated exposure of the patient to radiation energy is reduced or eliminated. Also desirable is a valve position verification device that is small, easy to use, and preferably portable. Preferably, the device can also monitor various valve functions without the necessity for additional energy means.
The present invention achieves the aforementioned goals by providing an acoustic monitoring system that is able to verify the valve positions of an implanted adjustable valve having a variable opening pressure, without the need for x-rays. The acoustic monitoring system is based on the observation that the mechanical motion due to the movement of the valve components sets up vibrations that lead to acoustic energy. Acoustic energies have been noted by listening to audible emissions while adjusting the valve. Accordingly, the present invention provides the clinician with an immediate indicator of the success or failure of an adjustment cycle by monitoring the acoustic energies generated by the valve during that adjustment cycle. The monitored energy is correlated with the command sent to the valve to determine the success or failure of the valve adjustment.
In one aspect of the present invention, a method is provided for verifying the position of a valve mechanism in an adjustable programmable valve in a patient. First, an acoustic monitoring system is provided. The acoustic monitoring system includes a programmer for generating a sequence of commands to adjust an opening pressure of the valve mechanism. The programmer is electronically coupled to a transmitter for receiving the commands, which transmitter is also electronically coupled to a sensor for detecting an acoustic signal generated from the valve mechanism during execution of the commands. Then, the location of the valve mechanism of the implanted valve is determined by the clinician. The transmitter is positioned over the valve mechanism and the sequence of commands from the programmer is initiated. The commands are sent to the transmitter, which then adjusts the valve mechanism accordingly. The acoustic signal generated from the valve is then detected by the sensor and transmitted back to the programmer. The programmer then analyzes the acoustic signal to confirm the position of the valve mechanism. Preferably, the programmer of the acoustic monitoring system generates an audible signal to confirm the success or failure of the adjustment. Visual confirmation can also be achieved by way of a message displayed on a panel or LCD.
To adjust the opening pressure of the valve mechanism, the sequence of commands from the programmer directs the transmitter to generate a magnetic field and apply this magnetic force to the valve mechanism. The valve mechanism can be of the type having a stepped motor, whereby adjustment is achieved by rotating the stepped motor. As the valve mechanism is moving, an acoustic signal is generated which is picked up by the sensor and translated to an electronic signal. The electronic signal can be relayed back to the programmer for analysis. The programmer can include a microprocessor for running a software that applies an algorithm for translating the acoustic signal into information for determining the success or failure of the adjustment cycle. The algorithm can classify the acoustic signal into clicks, bangs or other, for example. The algorithm then compares the actual streams of clicks and bangs detected from the transmitter to an expected stream of clicks and bangs to determine the success or failure of the adjustment cycle.
Once the programmer is done analyzing the electronic signal, an audible signal can be produced to indicate whether or not the command was properly executed. To maximize the ability of the sensor to detect the acoustic signal, ultrasound gel can be applied on the patient prior to positioning the transmitter. In one exemplary embodiment of the present invention, the sensor can be inserted into the transmitter after it has been positioned on the patient and over the valve mechanism.
In another aspect of the present invention, an acoustic monitoring device is provided for verifying the position of a valve mechanism in an adjustable programmable valve in a patient. The acoustic monitoring device comprises a housing having a top surface, a bottom surface, and a central opening extending through the bottom surface. A transmitter is contained within the housing. The transmitter has a plurality of electromagnetic coils for generating an electromagnetic field sufficient to rotate the valve mechanism of the adjustable programmable valve. The housing can have stainless steel feet extending from the bottom surface to help focus the electromagnetic field onto the valve mechanism. A tubular coupling member extends through the central opening of the housing. Seated on top of the tubular coupling member is an acoustic sensor, which is capable of detecting an acoustic signal generated by the valve mechanism during adjustment. The acoustic signal can be of the type consisting of bangs and clicks.
In other features of the present invention, the tubular coupling member extends beyond the bottom surface of the housing, and is configured to contact the patient""s skin. Furthermore, the acoustic sensor is mechanically isolated from the transmitter. Mechanical isolation can be achieved by having isolating pads or o-rings surrounding the outer diameter of the tubular coupling member. The isolating pads on the tubular coupling member prevent mechanical vibration of the housing from being transferred to the sensor. Yet another feature of the present invention is that the acoustic sensor can be configured to be inserted into the housing after the housing is positioned over the valve mechanism. In this way, the acoustic monitoring device can be modular, or built by the clinician during use. The tubular coupling rod can also be held in springing engagement within the housing, enabling movement with respect to the base of the housing. This feature allows self-adjustment of the coupling rod to the patient""s anatomy and optimizes the contact between the sensor and the patient.
Additionally, the acoustic monitoring device can include a power source for driving the electromagnetic coils contained within the housing. A signal amplifier, digitizing filter, and data storage unit can also be included within the housing for downloading the acoustic signal information to the programmer for analysis. Furthermore, the acoustic monitoring device can be configured for wireless communication for wirelessly transmitting the acoustic signal information to the programmer. For example, a wireless communication transmitter can be connected to the transmitter of the acoustic monitoring device to allow wireless transmission of the acoustic data to the programmer for analysis.